Reference copied to 'Dependencies' folder but still getting "The type or namespace name could not be found"

I cannot figure this out, in my module I added the reference to the library, when I run the orchard website, I can see that the dll is in the app_data/dependencies directory, yet in the code of my module (I have a @using directive for the library) my module
produces the error "The type or namespace name could not be found"

Has anyone had this problem? Am I doing something wrong? Any help would be much appreciated!